The French Government has been badly rattled by a corruption scandal known as the Clearstream affair in which senior politicians were accused, falsely, of having secret bank accounts.

The PM was accused of ordering a smear campaign against a rival

The origins of the scandal lie in defamatory letters sent to a judge by a mystery informant, and when it comes to anonymous tip-offs, the French have it down to a fine art.

The best vintage film rental shop in Paris, the estimable Videosphere by the Luxembourg Gardens, was unable to supply me last week with either of its two copies of Henri-Georges Clouzot's 1943 classic, Le Corbeau.

The film is inspired by events that took place in the town of Tulle after the World War I.

Life was turned upside down by a series of anonymous letters accusing prominent citizens of illicit love affairs.

The letters were signed "l'oeil de tigre" (the eye of the tiger) and the woman who sent them was eventually unmasked.

But when Clouzot made the film 20 years later, he changed the signature to Le Corbeau (the crow) and that is the word that has now entered the language to mean an anonymous and ill-intentioned informant.

Anyway, as the staff at Videosphere explained, a film which normally languishes for years on end on the shelves is suddenly back in hot demand.

France has been agog these last weeks to establish the identity of a new crow - the one who has lit a slow fuse under the government with his or her allegations of secret commissions and illicit offshore accounts.

Anonymous tip-offs

Anonymous letters and tip-offs are nothing new

It is not my intention here to go into the detail of the so-called Clearstream scandal, not least as it is so layered in lies and confusion as to be utterly unintelligible.

Suffice to say that it is good to see back in the headlines our old friend Monsieur le Corbeau and to remind ourselves of his many antecedents.

France actually has a word for the work of the corbeau: la delation, from the Latin delation.

In Roman times, a delator was an official who told the administration what tax money was owing, but the sense changed to mean informant or grass.

The practice of delation was widespread in the latter days of the French monarchy.

This was when kings would distribute their infamous "lettres de cachet" - orders for individuals to be locked up in the Bastille - often on the basis of anonymous tip-offs.

The system helped stoke the fires of the revolution, which of course brought informing to wholly different levels.

Unsolved murder

The heyday for French corbeaux, however, was much more recent: World War II.

A recent documentary claimed that an astonishing three million anonymous letters were sent to the German and Vichy powers denouncing neighbours as Jews, Communists, resistance members, profiteers or petty criminals.

The Germans themselves were said to be shocked by the extraordinary propensity of people to shop their fellow citizens.

Incidentally, after the war, Clouzot's film Le Corbeau was banned until 1969 because it was assumed to have been a comment on this stain on the nation's honour.

As the Clearstream affair shows, when a corbeau wants to act, he knows how to do it

Later, there was the 1984 murder of a four-year-old boy who became known as "le petit Gregoire".

Famously, the day after he was killed, his father received a corbeau letter saying: "I hope you die of grief. Money won't get your son back. This is my revenge."

No-one knows who sent the letter, and the crime remains unsolved.

And lest you think that I am talking about an isolated or purely historical phenomenon, let me quote a recent article in Le Monde, which said that every year the authorities still receive hundreds of anonymous denunciations, often of neighbours accused of dodging the taxman, or of illegally claiming benefits.

Dishing the dirt

It would be silly, of course, to pretend that France is alone in this, and in any case the line is fine between morally reprehensible delation on the one hand, and on the other, the duty to bring to light actual crimes.

To rebut the charge that delation is a national French characteristic, they could point to Britain's neighbourhood watch schemes and say they are a kind of snoopers' charter.

Nonetheless, the figure of the corbeau and the very word delation feature in the public consciousness in France in a way that they do not elsewhere, which prompts thoughts as to why.

The charitable answer - the one the French like to give - is that they are a Latin nation and they have always had a problem with authority, so it is hard for people to go publicly to the police with suspicions against their neighbours.

Possibly. But it prompts the rejoinder that in other Latin countries people have not been quite so diligent at anonymously dishing the dirt.

Perhaps it is to do with the nation's chronic instability, which means that people have little faith that the institutions of justice will work, so they give a little push for themselves?

Or is it a question of social relations? Is the frosty politeness with which people behave towards their neighbours a cover for festering resentments that need an outlet?

Like so much else in France, la delation is not what it used to be and that is a good thing.

But as the Clearstream affair shows, when a corbeau wants to act, he knows how to do it.

There is precedent and there is procedure.

No-one is that shocked or surprised when the crow caws.

From Our Own Correspondent was broadcast on Saturday, 3 June, 2006 at 1130 BST on BBC Radio 4. Please check the programme schedules for World Service transmission times.